1. Field of the Invention
The present invention relates to a nonaqueous electrolytic solution for a battery and a nonaqueous electrolytic solution battery. More particularly, the present invention relates to a secondary lithium battery comprising a nonaqueous electrolytic solution containing a predetermined halogen compound as a supporting electrolyte. Even more particularly, the present invention relates to a nonaqueous electrolytic solution for a battery which is arranged to prevent the production of hydrogen halide due to inevitable inclusion of a small amount of water content and a nonaqueous electrolytic solution battery comprising such a nonaqueous electrolytic solution.
2. Description of the Background
A nonaqueous electrolytic solution battery comprising lithium or a compound thereof as an active electrode material and therefore an organic solvent dissolving a supporting electrolyte therein as an electrolytic solution has been noted for its usefulness as a primary battery as a small-sized power supply for electronic parts or a secondary battery or lithium ion battery for electric automobiles.
Referring further to such a nonaqueous electrolytic solution battery, as the supporting electrolyte there is often used, e.g., halide such as LiPF.sub.6. However, if the electrolytic solution, which is supposed to be nonaqueous, inevitably contains some water content or has adsorbed water from other battery materials, the following reaction takes place to produce a hydrogen halide such as hydrogen fluoride HF. EQU LiPF.sub.6 +H.sub.2 O.fwdarw.2HF+LiF+POF.sub.3 (1)
Hydrogen fluoride deteriorates materials constituting the battery, causing further deterioration of battery properties. It is also known that the foregoing reaction (1) is accelerated at high temperatures. Therefore, these problems become remarkable when the nonaqueous electrolytic solution battery is used as a secondary battery for electric automobiles which must operate stably at a temperature of from -30.degree. C. to 60.degree. C. Thus, it is said that a nonaqueous electrolytic solution battery comprising LiPF.sub.6 as a supporting electrolyte can hardly be applied to such a use.
In order to overcome these difficulties, some proposals have been made. For example, JP-A-4-284372 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), which concerns an improvement in a nonaqueous electrolytic solution secondary battery, proposes that an oxide selected from the group consisting of Al.sub.2 O.sub.3, MgO and BaO, if incorporated in a nonaqueous electrolytic solution containing LiPF.sub.6 as a supporting electrolyte, adsorbs hydrogen fluoride produced in the electrolytic solution so that hydrogen fluoride is removed from the reaction system.
JP-A-7-122297, which concerns an improvement in a nonaqueous electrolytic solution battery, proposes that an acid anhydride (e.g., acetic anhydride), if incorporated in a nonaqueous electrolytic solution containing LiPF.sub.6 as a supporting electrolyte, previously catches water in the electrolytic solution to inhibit the foregoing reaction (1).
However, the above cited JP-A-4-284372 has some disadvantages. In accordance with duplicate experiments of the foregoing patent made by the present inventors, on the addition of some oxides to the extent within an actually acceptable amount for a battery, the removal of hydrogen fluoride proceeds too slowly to keep pace with the production of hydrogen fluoride. Accordingly, the foregoing proposal cannot effectively inhibit the deterioration of battery due to hydrogen fluoride.
On the other hand, the above cited JP-A-7-122297 exerts a high dehydration effect by an acid anhydride. As a result, however, an acid derived from the acid anhydride is produced. In other words, the foregoing proposal merely contemplates the substitution of other acids for hydrogen halide. Acetic acid or the like is relatively weaker than hydrogen halide but still deteriorates an electrolytic solution and battery can. Accordingly, the foregoing proposal provides no essential solution to the problems of the prior art.